// callback methods will be executed each time update panel ajax call is done
Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(function(sender, args){
});

Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(function (sender, args) {
});

Sys.WebForms.PageRequestManager.getInstance().add_endRequest(function (sender, args) {
});
